Supersonic jet fuel and method using iso-
paraffinic hydrocarbons and polycy-
clic hydrocarbons prepared from aro-
matic fractions



United States Patent Of ice Re. 26,116 Reissued Nov. 22, 1966 26,116 SUPERSONIC JET FUEL AND METHOD USING ISO- PARAFFINIC HYDROCARBONS AND POLYCY- CLIC HYDROCARBONS PREPARED FROM ARO- MATIC FRACTIONS Robert L. Barnes, Placentia, and Robert L. Dinsmore,

Long Beach, Calif., assignors to Richfield Oil Corporation, Los Angeles, Calif., a corporation of Delaware No Drawing. Original No. 3,177,653, dated Apr. 13,

1965, Ser. No. 242,888, Dec. 7, 1962. Application for reissue Mar. 23, 1966, Ser. No. 538,181

7 Claims. (Cl. 60-208) Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

The present invention relates to improved high energy fuels for supersonic aircraft, and, more particularly, relates to a blended high fuel density naphthenic type jet fuel.

High Mach number supersonic bombers, military fighters, and reconnaissance planes have severe fuel storage volume limitations which will affect the fuel capacity and range of such aircraft since thin wing section are utilized to minimize drag. Thus, supersonic transport and military aircraft, as well as long range commercial jets, require either additional fuel tanks for present fuels, or a fuel having a higher fuel density, that is, in terms of B.t.u.s/gallon of fuel.

Straight chain and/or branch chain aliphatic hydrocarbons and mixtures thereof have been employed for aircraft engines however, their fuel density is on the order of 115,000 B.t.u.s/gallon maximum. In the prior art it has been proposed to use as a high fuel density jet fuel the hydrogenated mixture of unsaturated polycyclic hydrocarbons boiling in the range of about 350 to 750 F. While such fuels have been found to provide higher heat of combustion per gallon, these fuels do not meet the viscosity or thermal stability requirements of military specifications for high Mach number jet fuels.

Accordingly, it is an object of the present invention to provide a high fuel density jet fuel having a heat of combustion of at least 130,000 B.t.u.s/gallon and a minimum of 18,400 B.t.u.s/lb.

It is also an object of the present invention to provide a high fuel density supersonic jet fuel having a low viscosity.

A further object of our present invention is to provide a high fuel density supersonic jet fuel of low viscosity having thermal stability.

Another object of the invention is to provide an improved method of operating jet engines.

Another object of my invention is to provide a method for making a high fuel density jet fuel.

Other objects and a more complete understanding of our present invention will become apparent in the present specification taken in conjunction with the appended claims.

Who have found that a blend of a mixture of decalin and alkyl decalins with about 10 to 25% hydrogenated propylene tetramer provides a high density fuel having satisfactory fuel density thermal stability and viscosity for supersonic aircraft. The decalins used in our present invention are preferably prepared from hydrogenated polycyclic hydrocarbons which have been extracted from a catalytically cracked side stream petroleum fraction boiling from about 400 to 520 F. This pertoleum fraction was found to be high in naphthalencs and the extract therefrom which may be used in the fuel of our present invention was found to contain substantially all naphthalene type aromatics which upon hydrogenation to complete saturation yielded an almost completely polynaphthene stock. The aromatic portion of the petroleum side stream fraction may be separated by any of the known extraction processes, including solvent treating methods and, for example, sulfur dioxide and silica gel extractions.

We have found that the 400 to 520 F. boiling range for the polycyclic aromatic fraction is critical in that higher boiling fractions do not have the thermal stability required and have widely varying viscosity characteristics. Lower boiling fractions have higher vapor pressures and reduce the B.t.u.s/gallon of the fuel blend such that it does not meet the proposed target specification (see Table I).

The aromatic extract is hydrogenated to substantially complete saturation according to our present invention by any conventional catalytic hydrogenation process. Fuels with substantial sulfur content may be hydrogenated with a two stage process utilizing first a desulfurization catalyst such as a cobalt-molybdenum, nickel-tungsten sulfide catalyst, etc., on a conventional alumina support with a second stage over nickel or platinum on a conventional support. Low sulfur stocks may be treated with a single stage hydrogenation utilizing only the nickel or platinum catalyst in accordance with conventional procedures. The product of the hydrogenation operation is a polynaphthene stock consisting essentially of decalin and alkyl decalins.

Properties of hydrogenated polycyclic aromatics are shown in Table I below, vis-a-vis a typical target specification for a high Mach number supersonic jet fuel. A target specification is not an actual fuel specification in the sense that a fuel must meet its requirements in order to be acceptable; rather, a target specification merely, as the name implies, gives direction to fuel manufacturers. As can be seen from these data, the viscosity of our decaline mixture is superior to that of the target specification. Several other low viscosity materials were used as blending agents to reduce the viscosity of the decalin mixture, however, the large majority of them either reduced the fuel density to a value below 130,000 B.t.u.s/ gallon or did not adequately reduce the viscosity of the blended fuel.

Thus, it was found that when hydrogenated propylene tetramer was utilized in amounts varying between 10 and 25%, the viscosity of the blended fuel was reduced to below 15 centistokes at 30 F., while the fuel density was not significantly lowered. The tetramer fraction utilized in the present invention has a boiling point in the range of 360 to 410 F. The use of tetramer as a blending agent to reduce the viscosity of the blended fuel without significantly affecting the fuel density is unexpected since the tetramer when added to a paraffinic stock having a viscosity similar to that of the polycyclic stock (decalin) does not reduce the viscosity of the resulting blended fuel. Accordingly, one would expect that it would expect that it would be necessary to utilize a less dense fuel in order to obtain a blended fuel having the desired viscosity.

As shown in Table I, the hydrogenated tetramer has a heat of combustion of 18,900 B.t.u.s/]b. and, hence, is also useful as a blending stock to increase the heat of combustion of the blended fuel.

The blending stock of the present invention may be any stock with low freezing point and viscosity blending characteristics and which is low in n-paralfins and high in isoparafiins, such as the above-mentioned tetramer fraction or any stock from which the n-parafiins have been extracted, as with molecular sieves or by treatment with urea. For example, the catalytically cracked stock may have the n-paraffins removed to the aromatic level followed by dewaxing to hold the freeze point of the aromatic stock, or the n-paraffins can be substantially 3 4 completely removed and the aromatic portion blended Net heat of comb., B.t.u./lb. 18,927 back with the dewaxed nonaromatic portion or another Luminosity No 113 highly isoparaifinic, dewaxed stock. Blending stocks Gravity 53.7 having boiling temperatures below the tetramer fraction Density, lbs./ gal 6.361 boiling range with correspondingly higher vapor pressures 5 Bromine number are not suitable as blending stocks since the resulting Bromine index Less than 10 blended fuel is subject to excessive fuel losses at high Composition by F.I.A., vol. percent: altitudes. Saturates 99.3 The thermal stability of the fuel may be measured Olefins 0.4 with a high temperature research coker at temperatures 10 Aromatics or olefins 0.3 in the range of 300 to 625 F. The side stream fraction ASTM distillation, F.: utilized with our present invention was found to be IBP 363 sufiiciently stable to pass the standard CFR coker test 367 without further treatment. 369 The freeze point of the blend fuel of our present inven- 15% 369 tion should be below 55 F. 370 371 EXAMPLE I 372 A low sulfur catalytically cracked stock from a Ther- 373 mofor Catalytic Cracking unit was taken as a side stream 0 3 5 from a bubble tower fractionation unit. This fraction 376 boiled between 400 and 520 F. and contained 4% 0% 37 naphthalenes, 9% alpha and beta methyl naphthalenes, 3 and 22% dimethyl naphthalenes for a total of 35% naph- 3 thaienes. The aromatic portion of this fraction was 25 p 407 separated by silica gel extraction and hydrogenated to complete saturation with a Raney nickel catalyst. The In the operation of jet engines with the fuels of the hydrogenated product consisted essentially of a mixture present invention, air is drawn from the atmosphere into of decalin and alkyl decalins. This product was blended an air compressor where it is compressed and approxiwith hydrogenated propylene tetrarner in amounts up to 30 mately one fourth of which is discharged int-o the combus- 25% of the blended fuel. The properties of the blended tion chamber (s) of the (gas turbine) engine where it is and unblended stocks are shown in Table I. mixed with the fuel of the present invention, ignited and Table I COMPARISON OF BLENDED AND UNBLENDED HIGH DENSITY NAPHTHENIC FUELS Target; Fuel #1 Tetramer Fuel #2 Fuel #3 Specifications Composition, Vol. ercent:

Hydrogenated -2 BTSS Fraction Hydrogenated Propylene Tetramer Inspections:

Smoke Point, mm Luminosity Number Thermal Stability. Thermal Decomposition Temperature. Vapor Pressure .2

()- Not Determined.

*Stablc to the extent tested-400 F. maximum.

Table II PROPERTIES OF HYDROGENATED PROPYLENE TETRAMEK Specific gravity, 60/60 F 0.7649 Existent gum, mg./ ml. 0.0 Accelerated gum, mg./l00 ml 0.0

Sulfur, percent 0.0012

Reid vapor pressure 0.6 Smoke point 50 Flash point, TCC, F 138 Pour point, F Below 1l0 Freezing point, F Below 1l0 Aniline point, F. 180 Viscosity at -30 F., cs 7.351

burned. The resulting hot combustion products are diluted with compresed air which has bypassed the combustion chamber, then joined with the combustion gases for cooling before reaching the first stage nozzle ahead of the first turbine. The hot gases are expanded in the turbine in such a manner that the power required to turn the compressor represents only a part of the total energy from the fuel. The high velocity hot gases expand through the turbines and reach terminal velocities at the exhaust nozzle. This produces thrust in accordance with Newtons 2nd and 3rd laws. The fuels of the present invention may also be used to operate turboprop engines in the same manner as above described except that the combustion mixture, prior to ejection through the exhaust nozzle, is expanded through a separate turbine which drives the propeller. The heat resistance of present construction materials limits the fuel to air weight ratios to approximately 0.0125 to 0.025. When richer mixtures are used, the temperatures produced at the first stage nozzle are beyond that which can be tolerated by the present construction materials.

The fuel of my present invention may be made by adding the hydrogenated tetramer to the hydrogenated polycyclic material or vice versa in any conventional refinery blending and mixing apparatus.

Although our invention has been described with a certain degree of particularity, the scope or our invention is not to be limited to the details set forth, but should be given the full breadth of the appended claims.

We claim:

1. A high fuel density blended jet fuel consisting essentially of hydrogenated polycyclic hydrocarbons prepared from a polycyclic aromatic fraction boiling in the range of 400 to 520 F. and from to 25 volume percent of hydrogenated propylene tetramer boiling in the range of 360 to 410 F.

2. A high density blended jet fuel consisting essentially of hydrogenated polycyclic hydrocarbons selected from the group consisting of decalin and alkyl dccalins prepared from a polycyclic aromatic fraction boiling in the range of from 400 to 520 F., and from 10 to 25 volume percent hydrogenated propylene tetramer boiling in the range of 360 to 410 F.

3. A high density blended jet fuel consisting essentially of hydrogenated polycyclic aromatic hydrocarbons selected from the group consisting of decalin and alkyl decalins prepared from a polycyclic aromatic fraction boiling in the range of 400 to 520 F., and from 10 to 25 volume percent of a highly isoparaffinic hydrocarbon boiling in the range of 360 to 410 F., said blended fuel having a fuel density of at least 130,000 B.t.u.s/gallon and a maximum viscosity of centistokes at 30 F.

4. A high density blended jet fuel consisting essentially of hydrogenated polycyclic aromatic hydrocarbons selected from the group consisting of decalin and alkyl decalins prepared from a polycyclic hydrocarbon fraction boiling in the range of 400 to 520 F. and 15 volume percent of a highly isoparafiinic hydrocarbon boiling in the range of 360 to 410 F., said blended fuel having a fuel density of at least 130,000 B.t.u.s/gallon and a maximum viscosity of 15 centistokes at 30 F.

5. A method of operating a jet engine which comprises feeding a mixture of air and a fuel consisting essentially of hydrogenated polycyclic hydrocarbons prepared from a polycyclic aromatic fraction boiling in the range of 400' to 520 F. and from 10 to 25 volume percent of hydrogenated propylene tetramer boiling in the range of 360 to 410 F., subjecting said mixture to combustion, passing the resulting hot combustion gases through a turbine to partially expand the gases therein, and then discharging the hot gases into the atmosphere through a nozzle to produce thrust.

6. A high density blended jet fuel consisting essentially of hydrogenated polycyclic hydrocarbons prepared from a polycyclic aromatic fraction boiling in the range of 400 to 520 F., and from 10 to 25 volume percent of a highly isoparaffinic hydrocarbon, said blended fuel having a fuel density of at least 130,000 B.t.u.s/gallon and a maximum viscosity of 15 centistokes at 30 F.

7. A high density blended jet fuel consisting essentially of hydrogenated polycyclic hydrocarbons prepared from a polycyclic aromatic fraction boiling in the range of 400 to 520 F. and from 10 to 25 volume percent of a dewaxed highly isoparaffinic hydrocarbon, said blended fuel having a fuel density of at least 130,000 B.t.u.s/gallon, a maximum viscosity of 15 centistokes at 30" F. and a freeze point of below F.

References Cited by the Examiner The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,105,351 10/l963 Stahy. 3,126,330 3/1964 Zimmerschied. 3,128,597 4/1964 Smith et a1.

CARL D. QUARFORTH, Primary Examiner.

B. R. PADGETT, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Reissue No 26, 116 November 22, 1966 Robert L, Barnes et aln It is hereby certified that error appears in the above numbered petent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 59, for "Whe" read M We column 2, line 57, strike out "would expect that it"; column 3, line 15, for "blend" read blended columns 3 and 4 Table I fourth column, line 3 thereof, for 5207" read 5387 --o Signed and sealed this 29th day of August 19675 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

